1. Field of the Invention
The present invention relates to an optical reflecting unit which is used in an image processing apparatus such as a scanner for reading a large copy or a large manuscript, and which is provided with a half mirror for leading a reflected light in the form of a line from the manuscript to a light receiving portion.
2. Prior Art of the Invention
Conventionally, in an image processing apparatus such as a scanner for reading a large manuscript, a light is irradiated to the manuscript, and a reflected light of one line extending perpendicularly to a running direction of the manuscript is read at once. The statement contents of the entire manuscript are optically read by reading per one line and by running of the manuscript.
In this case, the reflected light from the manuscript is led to a predetermined location such as a light receiving portion or the like. However, such optical system For leading the reflected light to a predetermined direction is provided with an optical reflecting unit having a half mirror.
FIG. 10 of the attached drawings is a cross-sectional view showing an arrangement of such conventional optical reflecting unit. As shown in FIG. 10, an optical reflecting unit 1 of this example comprises a support table 2 in the form of a triangular column extending in an elongated manner, and a half mirror 3 arranged on the support table 2 and fixedly arranged along a longitudinal direction on a slanting surface 2a having an inclination of, for example, 45 degrees.
With the above-described arrangement of the conventional example, an incident light A in the form of a line incident from the above in FIG. 10 is incident upon substantially a center of the half mirror 3 with respect to a width direction.
The incident light A is reflected by a surface of the half mirror 3, and a reflected light B thereof is incident upon a light receiving portion of a light receiving unit 4 that is a line sensor. The reflected light B is electrically transferred by the light receiving unit 4 to detect the incident light A.
For the optical reflecting unit 1 of the conventional example, however, the incident light A in the form of a line incident from the above has a part thereof which is reflected from the surface of the half mirror 3 and which is formed into the reflected light B. However, the remaining part of the incident light A is transmitted through the half mirror 3, and a transmitted light C thereof is incident upon the slanting surface 2a of the support table 2.
The slanting surface 2a of the support table 2 is formed into a planar surface so as to be able to securing or ensuring that the half mirror 3 is fixedly supported. For this reason, the transmitted light C incident upon the slanting surface 2a of the support table 2 has a part thereof which is reflected from the slanting surface 2a and which is again incident upon the half mirror 3. The incident transmitted light C exits the surface of the half mirror 3. The exiting transmitted light C is incident upon the light receiving unit 4 together with the reflected light B.
Accordingly, the following problem arises. That is, in the light receiving unit 4, a photoelectric transferred signal of the transmitted light C that is a disturbance light is overlapped with a detecting signal of the reflected light B to be detected originally. Thus, it is difficult to detect the incident lightA that is an object. Particularly, in a case where a level of the reflected light B is low, a signal/noise (S/N) ratio between the detecting signal of the reflected light B and the photoelectric transferring signal (noise) of the transmitted light C is deteriorated so that the subsequent signal processing becomes difficult.